diff --git a/arrays/src/arrays/Main.java b/arrays/src/arrays/Main.java
index 3959161..8af0809 100644
--- a/arrays/src/arrays/Main.java
+++ b/arrays/src/arrays/Main.java
@@ -1,7 +1,7 @@
 package arrays;
 
+import java.util.HashMap;
 import java.util.Iterator;
-import java.util.Queue;
 import tester.Tester;
 
 class Sieve implements Iterator<Integer> {
@@ -39,27 +39,46 @@ class Sieve implements Iterator<Integer> {
 
 class Sudoku {
     static boolean solved(int[][] puz) {
-        // First check the data is shaped correctly.
         if (puz.length != 9) return false;
-        for (int[] row : puz)
-            if (row.length != 9) return false;
 
         // Make sure they're all valid integers.
-        for (int[] row : puz)
+        for (int[] row : puz) {
+            if (row.length != 9 || isRepetitive(row))
+                return false; // Check row's the right length & there'ren't any
+                              // repeats.
             for (int n : row)
                 if (n < 1 || n > 9) return false;
-
-        // Check that there'ren't any repeats in a row.
-        for (int[] row : puz) {
-            for (int n : row) {}
         }
 
+        int[][] transposed = transpose(puz);
         // Check that there'ren't any repeats in a column.
-
-        // Check that there'ren't any repeats in a 3x3 square.
+        for (int[] col : transposed)
+            if (isRepetitive(col)) return false;
 
         return true;
     }
+
+    // Does the given array repeat itself?
+    static boolean isRepetitive(int[] arr) {
+        HashMap<Integer, Boolean> seen = new HashMap<>();
+
+        for (int n : arr)
+            if (seen.containsKey(n)) return true;
+            else seen.put(n, true);
+
+        return false;
+    }
+
+    // Return the transpose of a matrix. Assumes the matrix is properly shaped
+    // and sized.
+    static int[][] transpose(int[][] m) {
+        int[][] transposed = new int[9][9];
+
+        for (int i = 0; i < 9; i++)
+            for (int j = 0; j < 9; j++) transposed[j][i] = m[i][j];
+
+        return transposed;
+    }
 }
 
 class Examples {
@@ -99,12 +118,24 @@ class Examples {
             {7, 1, 3, 9, 2, 4, 8, 5, 6}, {9, 6, 1, 5, 3, 7, 2, 8, 4},
             {2, 8, 7, 4, 1, 9, 6, 3, 5}, {3, 4, 5, 2, 8, 6, 1, 7, 9}
         };
+        int[][] testPuz6 = {
+            {5, 3, 4, 6, 7, 8, 9, 1, 2},
+            {5, 7, 2, 1, 9, 6, 3, 4, 8}, // Two 5's in the same column.
+            {1, 9, 8, 3, 4, 2, 5, 6, 7},
+            {8, 5, 9, 7, 6, 1, 4, 2, 3},
+            {4, 2, 6, 8, 5, 3, 7, 9, 1},
+            {7, 1, 3, 9, 2, 4, 8, 5, 6},
+            {9, 6, 1, 5, 3, 7, 2, 8, 4},
+            {2, 8, 7, 4, 1, 9, 6, 3, 5},
+            {3, 4, 5, 2, 8, 6, 1, 7, 9}
+        };
 
         t.checkExpect(Sudoku.solved(testPuz1), true);
         t.checkExpect(Sudoku.solved(testPuz2), false);
         t.checkExpect(Sudoku.solved(testPuz3), false);
         t.checkExpect(Sudoku.solved(testPuz4), false);
         t.checkExpect(Sudoku.solved(testPuz5), false);
+        t.checkExpect(Sudoku.solved(testPuz6), false);
     }
     void testSieve(Tester t) {
         Sieve sieve = new Sieve(29);